1. Field of the Invention
The present invention relates to a substrate processing system for processing a substrate, such as a semiconductor wafer or a glass substrate for an LCD and, more particularly, to a substrate positioning unit included in a substrate processing system and. This invention further relates to a substrate positioning method.
2. Description of the Related Art
Generally a known semiconductor device fabricating process includes a step of coating a surface of a substrate, such as a semiconductor wafer, with a photoresist film, and a step of removing the photoresist film from the substrate. In those steps, a wafer is placed in a substrate processing unit in proper alignment relative to the substrate processing unit. The wafer is provided with a U-shaped or V-shaped alignment notch in its circumference. A substrate positioning unit generally called a notch aligner aligns the notch to a designated angle. The wafer thus aligned is carried into the substrate processing unit, such as a cleaning unit. The cleaning unit removes resist films and metal particles from the surfaces and the edge of the wafer, and dries the thus cleaned wafer.
Generally, a conventional notch aligner holds a wafer on an O ring placed on a rotating stage by suction, and rotates the wafer together with the rotating stage. Since the O-ring is in contact with the back surface of the wafer, it is possible that the wafer is contaminated with particles.
A prior art notch aligner disclosed in JP 2000-21956A supports a wafer by its periphery and detects an alignment notch formed in the circumference of the wafer. This prior art notch aligner is provided with a drop-in type rotating stage and a stationary stage. The rotating stage and the stationary stage each have three supporting parts on which a peripheral part of a wafer rests. The supporting parts are formed in outer end parts of narrow, radial arms radially extending from the centers of the rotating stage and the stationary stage, respectively. The arms of each of the rotating stage and the stationary stage are arranged at angular intervals of 120°. The rotating stage starts rotating from a predetermined reference angular position to determine the position of the alignment notch of a wafer supported thereon. When the position of the alignment notch could not be determined during the rotation of the rotating stage, the stationary stage receives the wafer from the rotating stage, turns through a predetermined angle, and then transfers the wafer to the rotating stage. Then, the rotating stage starts rotating from the reference angular position. Both the rotating stage and the stationary stage of the prior art notch aligner are rotatable, and the rotating stage can be vertically moved. Therefore, the prior art notch aligner has is large and has complicated construction. There is the possibility that the prior art notch aligner produces many particles because the same has many moving parts including rotating parts and vertically moving parts.
A holding member holds a wafer by its peripheral part in cleaning the wafer by using a spin chuck. A cleaning liquid has a difficulty in wetting parts, in contact with the holding member, of the wafer, so that it is possible that the parts in contact with the holding member cannot be satisfactorily cleaned. A spin chuck provided with a holding member that is operated by centrifugal force has been proposed to solve such a problem. The center of gravity of the holding member of this previously proposed spin chuck is determined properly such that the holding member does not hold the wafer while the spin chuck rotates for cleaning at a comparatively low rotating speed. However, when only a desired peripheral part of a wafer needs to be cleaned by using the spin chuck, the desired peripheral part cannot accurately be cleaned due to the eccentricity of the wafer.